require 'date'
puts y2k = Time.gm(2000, 1, 1) # => Sat Jan 01 00:00:00 UTC 2000
puts y2k + 1 # => Sat Jan 01 00:00:01 UTC 2000
puts y2k - 1 # => Fri Dec 31 23:59:59 UTC 1999
puts y2k + (60 * 60 * 24 * 365) # => Sun Dec 31 00:00:00 UTC 2000